Strong light-weight composites can be made by embedding various types of fibers or fabrics in a resin matrix. The polymer used for such a matrix is generally an epoxy resin, although several other resins such as phenolic, novolac, poly(ether-sulfone), poly(phenyl-sulfone), and bismaleimide resins have also been used for certain applications. As fibers or fabrics, carbon and graphite products have been quite useful in the composite structures.
The search for flame resistant materials to form laminates that can be used with greater safety in places such as aircraft cabins, has led to the selection of high temperature resins such as bismaleimides which have high anaerobic char yield (Scientific & Technological Aerospace Reprints, (1976), 14-16, Abstract N76-25354), and to the inclusion of phosphorus-containing compounds either in a mixture with or as an integral part of the resin used as matrix. Searle, in U.S. Pat. No. 2,444,536, discloses a widely used method for the preparation of maleimide polymers. As to the use of phosphorus-containing compounds, Kourtides et al. (Proceedings of the Adhesives for Industry Conference, El Segundo, CA, June 24-25, 1980) have shown substantial improvement in various properties of certain epoxy resins by preparing them with a bis(3-aminophenyl)methylphosphine oxide or its bisphenol analog, instead of the conventional diamine or phenol monomers or curing agents of the art. In summary, however, it can be stated that while the introduction of phosphorus into organic polymers has generally resulted in reduced flammability, increased adhesion, and better solubility in polar solvents, none of the resins used in the composite art are nonflammable.
In copending application Ser. No. 175,452, filed Aug. 5, 1980, entitled "Phosphorus-Containing Bisimide Resins", now U.S. Pat. No. 4,276,344 issued June 30, 1981, bisimides are prepared from phosphine oxides by a reaction typified by the following: ##STR1## The monomers (bisimides) 3 can be used to impregnate fibers and cloth and, upon curing to rigid composites, confer fire resistant qualities to the fiber or fabric reinforcement present in the composites.
It is an object of the present invention to provide improvements upon such monomers, polymers and impregnated fibers and fabrics.